Graphite lubricating composition of increased load carrying capacity



United States Patent 3,297 572 GRAPHITE LUBRICATIN-O COMPOSITION OF IN- CREASED LOAD CARRYING CAPACITY Arthur J. Haltner, Stralford-Wayne, Pa., and William G.

Luetzel, Scotia, N.Y., assiguors to General Electric Company, a corporation of New York No Drawing. Filed Sept. 1, 1964, Ser. No. 393,752

3 Claims. (Cl. 25229) This invention is related to the composition of improved dry lubricating films of graphite and more particularly to means for increasing the load carrying capacity of such films.

Graphite is now widely used as a solid lubricant and it is a primary object of this invention to increase the load carrying capacity of lubricating films of graphite in order to continue to expand the use of graphite as a solid lubricant.

Briefly stated, this invention is directed to the discovery that although most om'des and sulfides tested as additives to graphite were found to provide no significant improvement in the graphite films, a small number of these compounds (PbO Pb O MnO and FeS do produce significant improvement in the load bearing capacity of graphite films. Experiment has shown that this relatively small number of successful additive materials are able to significantly improve the maximum load carried by the graphite film, in some cases by a factor of at least two.

It is fortunate that the presence of these additives in the graphite film does not significantly alter the friction coefficient or the wear rate of the graphite film. With respect to the friction coetficient apparently any shearing phenomena in these films is confined to the graphite itself.

The techniques employed for studying the effect of these additives in graphite films were as follows. The substrate employed was mild steel which had been degreased, deoxidized and cathodically cleaned. The lubricant films (graphite plus additive) were rubbed on to the freshly cleaned metal surface. Generally several hours were required to obtain a satisfactory film. Data were taken in normal room air at about 24 C. and at a relative humidity of about 50% unless otherwise indicated. All rubbed films employed Asbury No. 280 graphite powder and the additive materials employed were the purest commercially obtainable. The films were tested by sliding a A3 diameter chrome alloy hemisphere thereover as the load on the hemisphere was increased in 50 grams increments. At the maximum load carried the graphite film ruptured and metal-to-metal contact occurred. The amount of additive employed in the test results tabulated herein was by weight, however, the effectiveness of these additives may be obtained using quantities thereof from an effective amount to about percent concentration by weight.

The data obtained in testing various sulfide additives are collected in Table I. Practically all of these materials had little or no effect on the load carrying capacity of the graphite films. The behavior of graphite films with FeS as the additive is illustrative of this type. Comparative tests have indicated that the performance of graphite films containing these additives with respect to load carrying capacity is very similar to the performance of a graphite film which contains no additive at all and there is no evidence that the addition of these sulfides has any effect, good or bad, on the durability of the film. Graphite films having no additive usually fail under the application of 2.0 kg. in the aforementioned test procedure. As seen in Table I it is only when FeS was employed that any significant improvement in load carry- 'ice ing ability was found in the graphite-additive films. Sb S had marginal value as an additive. The low friction value observed for WS as the additive probably reflects the excellent lubricating qualities of this sulfide and it can be expected that WS and graphite would form a compatible and useful lubricant much the same as M08 and graphite will form in combination. In the particular tests reported in Table I all additives were present in the concentration of 10 percent by weight TABLE I.EFFECT OF SULFIDE ADDIIIVES ON FRICTIONAL BEHAVIOR OF GRAPHITE FILMS Additive Max. Load (kg) #Film 2. 42 117 1. 92 109 2. 32 134 2. 22 118 1. 97 124 2. 69 095 2. 62 097 2. 39 131 2. 71 127 2. 54 127 2. 54 125 16 1. 40 088 2. 8 092 3. 14 101 3. 10 104 3. 60 120 4. 20 106 4. 80 104 4. 20 115 4. 50 110 2. 4 063 (min.) CuS+20% S 1.8

Similiar data is presented in Table II for those films having oxide additives for graphite films. Since it seemed feasible that the additive oxide would perform a role chemical in nature wherein the additive oxide, upon being reduced to a lower oxide or to the metal, would cause the formation of an oxide on the surface of the substrate, KClO was investigated. However, this additive proved to be only of marginal value. The average friction coefiicient for these graphite films is 0.10, a value very close to the friction coeflicient reported for graphite films (no additive).

TABLE II.-LOAD CARRYING ABILITY OF GRAPHITE FILMS CONTAINING OXIDE ADDI'IIVES Additive Percent RH. Max. Load, kg. p

Accordingly, it has been discovered that additives for graphite films chosen from the group consisting of PbO Pb O and MnO and FeS effectively increase the load carrying capacity of graphite films, when they are subjected to sliding action. Although the graphite lub-ri' cants containing the additives were rubbed 0n the metal surface in the above reported experiments and then burnished in to provide a strong adherent film, it is clear than other methods of application could be used. These methods would include the use of organic or inorganic binders and application by spraying dipping or brushing suspensions of the graphite lubricant and additive on the surfaces.

Since some commonly used bearing alloys contain antimony and since Sb S gives at least marginal improvement as an additive to a graphite film, one mechanism which may be employed is to deliberately sulfide the surface of such a bearing containing antimony to provide antimony sulfide. Thus, if a sulfiding agent is added to the graphite and applied as a film to the bearing substrate, antimony sulfide will then be provided in situ as the additive for the graphite layer. Such materials as AgS, PbS, AuS or H S (adsorbed) on the graphite could be incorporated in the graphite and would react with any freshly exposed antimony in the bearing surface to form Sb S which would adhere strongly to the graphite preserving the integrity of the graphite layer and, therefore, its load carrying capacity.

As supported by the preceding discussion a distinct and unobvious improvement has been made in the load bearing capacity of rubbed graphite films by determining those particular substances from the class of metallic oxides and sulfides, which perform in this manner, when employed as additives for the graphite in preparing these films.

Variations in the method of application or incorporation of these additive materials are contemplated, the invention residing in the choice of the particular additive materials disclosed herein. Thus, for example, a layer of the additive material may be placed on the metal first and a film of graphite may be rubbed thereover in much 4 the same manner as described for solid lubricant films in US. 3,127,346Oliver et al.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A dry lubricant composition comprising a mixture of graphite with at least one additive chosen from the group consisting of PbO Pb O MnO and FeS said additive being present in a concentration in the range of from a small amount to about 30 percent by weight, said small amount being eflective for substantially increasing the load bearing capacity of the graphite.

2. A dry lubricant composition as recited in claim 1 wherein the additive is MnO 3. A dry lubricant composition as recited in claim 1 wherein the additive is FeS References Cited by the Examiner UNITED STATES PATENTS 1,895,756 1/1933 Fuller 252-42 2,421,543 6/1947 Cook 25225 2,470,264 .5/ 1949 Richardson 252-12 3,059,769 10/1962 Frost 252l2 OTHER REFERENCES Scientific Lubrication, March 1957, page 36.

References Cited by the Applicant UNITED STATES PATENTS 3,127,346 3/1964 Oliver et al.

DANIEL E, WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner. 

1. A DRY LUBRICANT COMPOSITION COMPRISING A MIXTURE OF GRAPHITE WITH AT LEAST ONE ADDITIVE CHOSEN FROM THE GROUP CONSISTING OF PBO2, PB3O4, MNO2 AND FES2, SAID ADDITIVE BEING PRESENT IN A CONCENTRATION IN THE RANGE OF FROM A SMALL AMOUNT TO ABOUT 30 PERCENT BY WEIGHT, SAID SMALL AMOUNT BEING EFFECTIVE FOR SUBSTANTIALLY INCREASING THE LOAD BEARING CAPACITY OF THE GRAPHITE. 